4 The Unity of the Organism 



seminal-atoms, connected and diffused throughout the veins, 

 the viscera and the nerves." Then comes a discourse on the 

 nature of the soul substance: "Nor jet is this nature or 

 substance to be regarded by us as simple and uncom- 

 pounded. For a cert~ain subtle aura, mixed with heat, leaves 

 dying persons ; the heat moreover, carries air with it. . . . 

 Nor yet are all these constituent parts, aura, heat, and air, 

 sufficient to produce mental sense or power. A certain 

 fourth nature or substance must therefore necessarily be 

 added to these : this is wholly without a name ; it is a sub- 

 stance, however, than which nothing exists more active or 

 subtle, nor is anything more essentially composed of small 

 and smooth elementary particles ; and it is this substance 

 which first distributes sensible motions through the mem- 

 bers. . . . This fourth principle lies entirely hid, and re- 

 mains in secret, within ; nor is anything more deeply seated 

 within the body ; and it is itself, moreover, the soul of the 

 whole soul." ^ 



The further need our enterprise has to draw upon history 

 as such permits us to leap across nearly eighteen centuries, 

 for the next occurrences touching these theories which 

 greatly concern us belong to the period of splendid achieve- 

 ment in the sciences of living beings from Linnaeus' System 

 of Nature to Darwin's Origin of Species. The course of 

 thinking and discovery during this period has been so in- 

 terpreted as to appear to constitute a virtual proof of the 

 correctness of the elementalist theor3^ It is said that in the 

 Linnean era plants and animals were treated from the 

 standpoint of the organism as a whole, and that later, under 

 the chieftainship of Cuvier, "instead of the complete or- 

 ganism, the organs of which it is composed became the chief 

 subject of analysis." Then, w^ith Bichat leading, came tlie 

 advance to the tissues ; then before long the discovery w^as 

 made that not the tissues but the cells are the real units 

 of structure, Schleiden and Schwann being foremost in this 



